This invention relates to an electronic balancing system for balancing road vehicle wheels, and in particular to a balancing system of the type wherein wheels can be balanced without removing them from the vehicle.
It is a well known fact that, nowadays, wheels are balanced using one of two different types of apparatus, one type allowing wheels to be balanced while removed from the vehicle, and the other affording the possibility of balancing a wheel while mounted to the vehicle in its natural operative emplacement. Since with the latter type, wheels are balanced in their natural emplacement and in conditions approximating the actual operation ones, it is undoubtedly the most accurate. In fact, owing to the wheels being balanced on the former type of apparatus while separated from the vehicle structure, the wheels, upon re-installation on the vehicle, are caused to occupy, owing to the gravity force, a different mounting position with respect to the rotation center from the one they had while connected to the balancing machine, this different position being a source of unbalance. Moreover, those parts which are to rotate rigidly with the wheels are not balanced, and this is an added source of unbalance. Notwithstanding the inaccuracy of the balancing achieved thereby, the apparatus which are suitable for balancing disassembled wheels still enjoy wide acceptance, because the ones intended for balancing wheels in their mounted condition are difficult to operate and require more time.
Thus, the need is felt in this field for a mounted wheel balancing machine which, while retaining highly accurate balancing capabilities, is not only adapted to eliminate the cited sources of difficulties in operation, to make the balancing operation a straightforward one which can be tackled by any unskilled operator, but also reduces the operation time.
The apparatus for balancing wheels while mounted to the vehicle, in spite of their varied configurations, are all inspired by the same principle, and the balancing operation is carried out in the same basic manner: the wheel to be balanced is raised from the ground by means of a jack placed under the vehicle and, at any point on the outer wall of the tire, a reference mark is applied, with chalk or a length of adhesive tape, quite often the inflating valve itself being taken as the reference mark; in this respect, reference can be made to U.S. Pat. No. 3,070,720.
A pulse transducer is placed under the vehicle as close as possible to the wheel to be balanced; some transducers are intended for resting with one end on the ground and the other end against the vehicle, whereas others do not rest on the ground but are attached, by means of a magnet, under the vehicle, still others being incorporated in the jack or lifting device itself. The transducer is connected to the balancer or balancing machine, which generally comprises an unbalance indicator gauge and a stroboscopic lamp, the wheel to be balanced, if not a driving one, being rotated by means of a pulley connected to a motor, and if a driving one, by the vehicle own engine. If the wheel is unbalanced, the pick up device placed under the vehicle wheel, at each revolution, when the unbalancing and hence heavier portion is lowermost, receive an impulse which, when converted into an electric pulse, is transmitted to the stroboscopic lamp or light and to the unbalance indicator gauge; the former will then light up, and owing to the stroboscopic effect, show the wheel as if it were standing still, while the latter will show the extent of the unbalance, which varies according to the wheel r.p.m.; the location of the mark applied to the wheel must be detected at the precise instant when the gauge reads a maximum of unbalance. Once these measurements have been taken, the wheel is stopped, and the mark applied to the wheel is brought back to the position where it had been sighted at the moment of maximum unbalance, and to the topmost portion of the wheel, which corresponds to twelve o'clock, a counterweight is attached, the weight whereof has been indicated on the meter. It will be apparent how, with this balancing system, one has to simultaneously detect two different indications which are apart from each other and moving, because both the meter pointer and the mark on the wheel vary simultaneously with the speed.
This need for simultaneously surveying two points placed apart from each other makes the balancing operation a difficult one. In the instance of driving wheels, to these difficulties, there adds the need for a second operator, who is to stay on the vehicle and rev up and down as required, while the other operator on the ground has to read the extent of the unbalance on the meter and detect the mark on the wheel.
To obviate such drawbacks, as taught for example by German Pat. No. 1,698,111, a photoelectric cell device has been also developed, wherein in addition to the transducer placed under the vehicle, a photoelectric cell transducer is placed in front of the wheel to be balanced and detects the passing of the mark applied to the wheel with chalk or any other suitable marking material. The electric signal correspondingly issued is phase compared, through a suitable electronic circuitry, to the signal from the unbalance transducer. Thus, a voltage is produced which is proportional to the displacement angle and is applied to a motor, to the shaft whereof the slider of a potentiometer and a disk with a pointer are keyed. A negative feedback system, comprising the voltage drawn from the slider of said potentiometer by a differential amplifier, causes the pointer to form, with a reference index, an angle equal to the angle between the signals from the two transducers. Briefly, the apparatus taught by the cited German Pat. No. 1,698,111 provides a slave mechanism wherein a pointer moves similarly to the chalk mark in the traditional stroboscopic devices. The usefulness of such a slave machanism resides in that the two points which the operator is to sight are brought closer to each other, thereby the driving wheel balancing can be performed by one operator. Notwithstanding the advantages mentioned, that apparatus or mechanism is a complex one, and falls short of solving the problem of a quickly and simply carried out balancing operation. In fact, before the correct weight and position are found, the operation must be repeated several times, like with the stroboscopic light apparatus.
Another vehicle wheel balancing apparatus, of the type suitable for balancing wheels in their mounted condition, is disclosed in U.S. Pat. No. 4,109,532 by the same applicant. That apparatus comprises mechanical impulse pick-up means which are adapted, when suitably positioned close to an unbalanced wheel being rotated, for receiving at each revolution thereof a mechanical pulse and converting said mechanical pulse into a corresponding electric pulse of unbalance, unbalance indicating means circuit connected to said pick-up means to receive therefrom, at each revolution of said wheel, said electric pulse of unbalance, said indicator means being adapted for storing the electric pulse from said pick-up means which corresponds to the maximum amount of unbalance of said wheel, unbalance position detecting means circuitally connected to said pick-up means to receive therefrom, through control circuit means, electric pulses of unbalance which correspond to said mechanical pulses, and adapted to be energized by said electric pulses and to cooperate with said unbalance indicating means for detecting the position of said unbalance in said wheel, and including a position of unbalance indicating disk which is adapted to be removably associated with said wheel to cooperate with said unbalance position detecting means and with the unbalance indicating means to provide the position of said unbalance in said wheel, and display means operative to display the exact position of said unbalance in said wheel as indicated by the position of unbalance indicating disk.
With the apparatus of U.S. Pat. No. 4,109,532, the balancer proper is placed in front of the disk, after the latter has been attached to the wheel. The balancer, in addition to the unbalance and position indicating gauges, further comprises two photocells, which are directed against the disk. As the wheel rotates, the first photocell is energized by the passage of the zero-indicating mark. Simultaneously therewith, the second photocell starts counting the series of spaced marks to store in the digital meter the number corresponding to the mark whereat maximum unbalance occurs. After stopping the wheel, at the stored number position, a counterweight is applied the weight whereof is read on the second gauge.
While that apparatus has proved satisfactory, it still shows some complication in use, such as the need for positioning the cited disk onto the wheel to be balanced. In fact, the disk could not be a single or standard one, but had to be changed in conformity with the type of rim of the wheel to be balanced, thereby the apparatus had to be equipped with a plurality of such disks, which must be selected each time by the operator performing the balancing.